Sodium heated steam generator

ABSTRACT

A sodium heated steam generator in which the likelihood of tube failure from such factors as thermal growth is reduced and in which in the event of a tube failure the products of a sodium water reaction are quickly exhausted out of the steam generator. Water is generated to steam in bayonet tube assemblies extending downward into a vessel down through which liquid sodium flows and into which a central relief channel extends to provide means for the escape of the products of an accidental sodium water reaction.

United States Patent 1 Barratt SODIUM-HEATED STEAM GENERATOR [75] Inventor: Robert 0. Barrett, Parsippany, NJ.

[73] Assignee: Foster Wheeler Corporation,

Livingston, NJ.

[22] Filed: Mar. 3, 1971 [21] Appl. No.: 120,434

52 us. Cl. 122/32, 165/142 [51] Int. Cl. F22b 1/16 [58] Field of Search 122/32, 34, 483; 165/ 142, 145

[56] References Cited UNITED STATES PATENTS 3,685,626 4/1963 Bognaret a1. 165/142 X 3,090,433 5/1963 Amorosi et a1. 165/142 X 3,279,439 10/1966 Ammon 122/483 X 1 June 26, 1973 3,613,781 10/1971 Barratt 122/32 Primary Examiner-Kenneth W. Sprague Attorney-John Maier, Ill, Marvin A. Naigur and John E. Wilson 571 ABSTRACT A sodium heated steam generator in which the likelihood of tube failure from such factors as thermal growth is reduced and in which in the event of a tube failure the products of a sodium water reaction are quickly exhausted out of the steam generator. Water is generated to steam in bayonet tube assemblies extending downward into a vessel down through which liquid sodium flows and into which a central relief channel extends to provide means for the escape of the products of an accidental sodium water reaction.

6 Claims, 4 Drawing Figures PATENTED JUN 2 6 I975 SHEET 1 OF 2 INVENI'OR. ROBERT O. BARRATT ATTORNEY PATENTED JUN 2 6 I975 SHEETZBFZ MENTOR. ROBERT O. BARRATT 4% T'IORNE Y SODIUM-HEATED STEAM GENERATOR BACKGROUND OF THE INVENTION The most familiar type of nuclear power plant utilizes liquid sodium to cool the reactor and to transfer heat to water to make steam. Such a system presents a safety hazard because liquid sodium must be brought into indirect heat exchange with water. In the event of a material failure, the liquid sodium and water could come into contact with the result of an explosion due to the consequent sudden rise in pressure. The possibility of a liquid sodium reaction is ever present because of the thermal growth of the components in the steam generator and because of the erosion and corrosion which are concomitant with the use of flowing sodium.

Still another problem found in sodium heated steam generators is the problem of sodium stagnation caused by a lack of agitation in the sodium flowing through the generator. The prevention of sodium stagnation increases efficiency and reduces the chances of tube overheating and failure.

SUMMARY OF THE INVENTION which the bayonet tube assemblies extend so that liquid sodium flowing downward flows axially inward and alternately outward across the bayonet tubes until it reaches the bottom of the vessel. In the event of an accidental sodium water reaction, the relief channel is adapted to exhaust the product of the reaction quickly out of the vessel to prevent a violent explosion.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a front view partly'in section of a sodium heated steam generator made in accordance with the present invention;

FIG. 2 is a fragmentary view showing several of the bayonet tubes of FIG. 1;

FIG. 3 is a top view partly in section taken substantially along the line 33 of FIG. 1; and

FIG. 4 is a top view partly in section taken substantially along the line 4-4 ofFIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT There is shown in FIG. 1 a sodium heated steam generator indicated generally as 10. It consists of a pressure vessel 12 which is flared inwardly at 14 to provide a bottom and which has at its upper end a head section 16 with a lower flange 18 which is connected to a flange 20 of the pressure vessel. The head section 16' includes an annular chamber 22 which is defined by an inner vertical wall 24 and an outer vertical wall 26 and an annular head 28 which is secured to the top of the head section to completely enclose the annular chamber 22. An annular upper tube sheet 30 extends across the annular chamber 22, being secured at its marginal portions between the head-28 and the tops of the inner vertical wall 24 and the outer vertical wall 26. The upper tube sheet 30 divides the annular chamber 22 into an upper chamber 32 and a lower chamber 34. The lower chamber 34 is defined by the inner vertical wall 24, the outer vertical wall 26, the upper tube sheet 30, and a lowerv annular tube sheet 36.

Extending downwardly from the head section 16 and into the pressure vessel 12 are a series of bayonet tube assemblies 40. The bayonet tube assemblies comprise an inner tube 42 and an outer tube 44. Several. of these assemblies are shown well in FIG. 2. Each of the inner tubes 42 extends upwardly to the upper tube sheet 30. Each of the outer tubes extends upwardly to the lower tube sheet 36. Although the bottoms of the bayonet tube assemblies 40 are not shown in detailin the drawings, it will be understood thatthe lower ends of the outer tubes 44 are closed while the lower ends of the inner tubes 42 extend almost to the; ends of the outer tubes butare open. As shown in FIG. 2, spiral fins extend down between the inner tube 42 and the outer tube 44 of each of the tube assemblies 40. This prevents departure from nucleate boiling, that is the accumulation of steampockets which create areas of little heat absorption and consequent failure of the outer tubes. It has already been explained that it is necessary to prevent, as'much as possible, tube failure which would result in a sodium-water reaction.

Water inlets 48 allows water to enter the upper chamber 32 and flowdownwardly through the inner tubes 42 and to return upwardly between the inner tubes 42 and outer tubes 44 to be transformed into steam. The steam will collect in the lower chamber34 and then flow out through steam outlets 50 for ultimate use as in a steam turbine.

The liquid sodium which is used to generate the steam is directed into the pressure vessel 12 through sodium inlets 52 and is allowed to flow downwardly through the pressure vessel 12 through a perforated flow distribution sheet 54 to a lower chamber 56 and out of the pressure vessel 12 through a sodium outlet 58.

In order to insulate the pressure vessel 12 from the extremely high temperatures of the incoming sodium a flow shroud 60 is provided. The flow shroud 60 is generally cylindrical in configuration but has an inwardly flared bottom 62 which directs the downflowing so-.

dium to the sodium outlet 58. As shown in FIG. 1, the flow shroud 60 is spaced inwardly from the pressure vessel 12 and extends to a location slightly above the sodium inlet 52. Sodium entering through the sodium inlet 52 will flow primarily upwardly over the flow shroud but some of it willflow down between the flow shroud 60 and the pressure vessel 12 to completely fill the space between those two members. During operation this space will be completely filled with sodium which will insulate the pressure vessel 12 from the high temperatures of the sodium being received by the steam generator 10.

The interior surface of the sodium inlet and most of the interior surface of the pressure vessel 12 are covered with a stainless steel liner 64 which in the event of a leak in the flow shroud 60 will delay the sodium before it starts burning through the pressure vessel 12 for a time longenough for instrumentation to indicate the existence of the leak and emergency procedures to be executed. A suitable system would, for example, detect the presence of hydrogen which is released as the liquid sodium burns through the stainless steel liner 64. With adequate warning the water and sodium in the generator can be withdrawn to prevent damage caused by the pressure created by a larger sodium water reaction. The hot sodium flowing over the flow shroud 60 will flow downward over the bayonet tube assemblies 40 in an inward and alternately outward flow path due to a series of baffles.

In order to assure crossflow of the liquid sodium over the bayonet tube assemblies 40, inner baffles 66 and outer baffles 68 are provided. The inner baffles 66 are spaced along the length of the generator alternately with the outer baffles 68. One of the outerbaffles 68 is shown in plan in FIG. 3. It extends inwardly from the flow shroud 60 to a circle midway between the shroud and one of a series of axially spaced collars 70 the function of which will be described presently. In order to assure rigidity, inwardly extending webs permit the outer baffles 68 to be connected with the collars 70.

FIG. 4 shows one of the inner baffles 66. It is connected at a web 74 to one of the collars 70 and extends outwardly to its periphery 76. The baffles 66 and 68 are connected with each other and with the perforated flow distribution sheet 54 and the lower tube sheet 36-by means of tie rods 80. The alternate spacing of the inner baffles 66 and outer baffles 68 assures that the sodium will flow across bayonet tube assemblies 40 throughout the length of its travel down the steam generator to the sodium outlet 58.

The-bayonet tube assemblies 40 are not secured to the baffles 66 and 68 but pass through them loosely enough to permit the bayonet tube assemblies to expand and contract without imparting stresses to the surrounding structure. The use of bayonet tubes which are secured only at one of their ends to a tube sheet and which are slidably secured to the baffles which are secured by a tie rod only at one end to a fixed tube sheet has minimized the'thermal growth problems which in many sodium heated steam generators create the hazard of tube failure and its consequent sodium water reaction.

It has already been explained that in spite of precautions such as those discussed above, tube failure and consequent sodium water reaction is an ever present possibility. In order to relieve the present steam generationed within the sodium outlet 58. The sodium in the annular space between the bottom 14 of the pressure vessel and the inwardly flared bottom 62 of the flow shroud 60 is restrained from moving into the sodium outlet by plates 86. The plates 86 extend alternately flared bottom 62 and a flange 88 mounted on a seat 90 "on the'bottom 14 of the pressure vessel 12. This creates tor of the products of such a reaction and thereby eliminate the possibility of an explosion, the collars 70 which define a central relief channel 81 having a series of one way valves which consist of trap doors 82 connected with the collars 70 to open only upwardly. In the event of a sodium water reaction the doors open to allow sodium and the products of the reaction through the channel 81 and flow upwardly unobstructed to a location where it can be safely treated. During normal operation, the doors remain closed so that downward flowing sodium'can, at the level of each pair of doors 82, flow only at a location radially out from the channel 81 because of the barrier created by the doors 8l,'coland 68 thus insure cross-flow of sodium across the bayonet tube assemblies 40 and induce enough agitation to prevent sodium stagnation.

After flowing through the perforated flow distribution sheet 54, the liquid sodium flows through the ana seal and permits the insides that is the entire generator 10 other than the shell 12 and its bottom 12, to be lifted out for inspection or repair without breaking any parts at the lower seal. Similarly the insides can be lowered into place and will seal because'the plates 86 will intermesh and prevent sodium flow.

The steam generator is supported by supports 94 which are connected at a location fairly high on the steam generator 10 to prevent it from toppling even in the event of an earthquake. To prevent the steam generator from swinging in such an eventuality the steam generator can be supported laterally in the vicinity of the perforated flow distribution sheet 54. The sheet 54 will transmit forces received externally about the shell 12 and flow shroud 64 through-projections 96 which project radially outward from the flow shroud 64 toward the shell 12. The projections 96 do not contact the shell 12 but in the event that an excessive external lateral force should be exerted in the vicinity of the perforated flow distribution sheet, the projection 96 and possible and modifications can be made without exceeding the scope of the present invention as defined in the following claims.

What is claimed is:

l. A sodium heated steam generator comprising an elongated vertically extending pressure vessel, a plurality of bayonet tube assemblies extending longitudinally of and within said pressure'vessel, said bayonet tube assemblies each having an outer tube closed at its lower end and open at its upper end and an inner tube open at both ends positioned within said outer tube, an upper tube sheet and a lower tube sheet, said inner tubes extending to said upper tube sheet, said outer tubes extending to said lower tube sheet, a water inlet above -said upper tube sheet and a steam outlet between said upper tube sheet and said lower tube sheet, a liquid sodium inlet below said lower tube sheet and a liquid sodium outlet at the lower portion of said generator, a central flow channel at the longitudinal axis of said generator for releasing the products of an accidental so-' dium water reaction, said flow channel having a series of axially spaced collars bridged by doors which open from said means, and outer baffles spaced alternately with respect to said first defined baffles and permitting r upper end of said flow shroud extending above said'sodium inlet so that sodium flowing into said generator through said inlet will flow upwardly over said shroud and then downwardly over said baffles'and said bayonet tube assemblies.

4. The steam generator defined in claim 3 further comprising a pressure vessel, said flow shroud being positioned within said vessel with a small vertical annular space between said shroud and said vessel so that a portion of said sodium coming through said sodium inlet will flow downward in said space until said space is filled with sodium.

5. The steam generator defined in claim 4 wherein said outer baffles are joined at their outer periphery with said flow shroud.

6. The steam generator defined in claim 5 wherein said flow shroud and pressure vessel are flared inwardly at the bottoms thereof and further comprising plates extending down from said bottom of flow shroud, and plates extending upward from the bottom of said pressure vessel, said upwardly extending plates being intermeshed with said downwardly extending plates. 

1. A sodium heated steam generator comprising an elongated vertically extending pressure vessel, a plurality of bayonet tube assemblies extending longitudinally of and within said pressure vessel, said bayonet tube assemblies each having an outer tube closed at its lower end and open at its upper end and an inner tube open at both ends positioned within said outer tube, an upper tube sheet and a lower tube sheet, said inner tubes extending to said upper tube sheet, said outer tubes extending to said lower tube sheet, a water inlet above said upper tube sheet and a steam outlet between said upper tube sheet and said lower tube sheet, a liquid sodium inlet below said lower tube sheet and a liquid sodium outlet at the lower portion of said generator, a central flow channel at the longitudinal axis of said generator for releasing the products of an accidental sodium water reaction, said flow channel having a series of axially spaced collars bridged by doors which open only upwardly, said bayonet tube assemblies being positioned radially of said channel, a plurality of annular baffles extending outwardly from said channel with said bayonet tubes extending loosely through said baffles, said baffles including inner baffles each extending outward from one of said collars permitting sodium to flow downward in substantial quantity only when spaced from said means, and outer baffles spaced alternately with respect to said first defined baffles and permitting said sodium to flow downwardly only when adjacent to said means.
 2. The steam generator defined in claim 2 further comprising a plurality of tie rods secured to said lower tube sheet and extending downwardly through said baffles, said baffles being connected to said tie rods.
 3. The steam generator defined in claim 2 further comprising a flow shroud, said flow shroud extending vertically and spaced outwardly from said channel, the upper end of said flow shroud extending above said sodium inlet so that sodium flowing into said generator through said inlet will flow upwardly over said shroud and then downwardly over said baffles and said bayonet tube assemblies.
 4. The steam generator defined in claim 3 further comprising a pressure vessel, said flow shroud being positioned within said vessel with a small vertical annular space between said shroud and said vessel so that a portion of said sodium coming through said sodium inlet will flow downward in said space until said space is filled with sodium.
 5. The steam generator defined in claim 4 wherein said outer baffles are joined at their outer periphery with said flow shroud.
 6. The steam generator defined in claim 5 wherein said flow shroud and pressure vessel are flared inwardly at the bottoms thereof and further comprising plates extending down from said bottom of flow shroud, and plates extending upward from the bottOm of said pressure vessel, said upwardly extending plates being intermeshed with said downwardly extending plates. 